1. Technical Field
The invention relates to digital processing apparatus and method which are suitable for use in a system which performs broadcasting by a stream of MPEG (Moving Picture Coding Experts Group) 2 like digital satellite broadcasting or digital terrestrial broadcasting. More particularly, the invention relates to such apparatus and method which enable a plurality of simultaneously broadcasted programs to be received without changing a CA (Conditional Access System) system, thereby enabling recording of a back program in the same time slot on a different channel, reproduction of a multiscreen, PinP (Picture in Picture) reproduction, or the like.
2. Background Art
In Japanese digital broadcasting (digital satellite broadcasting, digital terrestrial broadcasting, digital CATV (Cable Television)), an MPEG2 system (ISO/IEC 13818-1 GENERIC CODING OF MOVING PICTURES AND ASSOCIATED AUDIO: SYSTEMS Recommendation H. 222.0) is adopted. Such a system has been formed on the basis of the standards of ARIB (Association of Radio Industrial and Businesses).
According to the MPEG2 system, a system for multiplexing individual streams of encoded video/audio, additional data, and the like and reproducing them synchronously with one another has been specified. There are two types of systems such as MPEG2-PS (Program Stream) and MPEG2-TS (Transport Stream).
Since the MPEG2-PS has been made on the assumption that it is applied to transmission and storage of data in an environment where no errors occur and redundancy can be reduced, it is used in a digital storage media such as a DVD (Digital Versatile Disc) or the like using a powerful error correction code.
The MPEG2-TS has been made on the assumption that it is applied to an environment such as broadcasting, communication network, or the like where a transmission error of data occurs, and a plurality of programs can be constructed in one stream. Therefore, the MPEG2-TS is used in digital broadcasting or the like.
In the MPEG2-TS, a plurality of TS (Transport Stream) packets of a fixed length of 188 bytes are collected so as to construct a transport stream. The length of TS packet of 188 bytes has been determined in consideration of matching performance with a length of ATM (A synchronous Transfer Mode) cell.
The TS packet is constructed by a packet header of a fixed length of 4 bytes and an adaptation field and a payload of a variable length. A PID (packet identifier) and various flags have been defined in the packet header. The type of TS packet is identified by the PID.
A PES (Packetized Elementary Stream) packet in which the individual streams of video, audio, and the like have been enclosed is divided into a plurality of TS packets having the same PID numbers and transmitted. For example, the MPEG2 system is used for encoding the video data. An MPEG2-AAC (MPEG2 Advanced Audio Coding) system is used for encoding the audio data in, for example, BS (Broadcast Satellite) digital broadcasting.
The PES packet in which data such as subtitles and the like has been enclosed is also divided into a plurality of TS packets and transmitted in a manner similar to the packet of video and audio.
Further, a packet of information of SI (Service Information) described by a table in a section format is contained in the transport stream. There is PSI (Program Specific Information) as SI for all stations. The PSI is information necessary for a system which selects and receives a program of a desired broadcast. As such information, there are a PAT (Program Association Table), a PMT (Program Map Table), an NIT (Network Information Table), a CAT (Condition Access Table), and the like.
A PID and the like of the PMT corresponding to the program number have been described in the PAT. Video data, audio data, and additional data included in the corresponding program, and the PID of a PCR are described in the PMT. A carrier frequency at which a target program is transmitted has been described in the NIT. Information regarding identification of a limited receiving system and information regarding individual information such as contract information or the like are described in the CAT. There is an EIT (Event Information Table) as SI which is used for services of a broadcasting company. A broadcasting schedule of programs has been described in the EIT. The EIT is used for an EPG (Electronic Program Guide) or recording reservation.
As digital broadcasting of such an MPEG2 system, digital CS (Communication Satellite) broadcasting and digital BS (Broadcast Satellite) broadcasting have already been started. In the digital BS broadcasting, broadcasting of an HDTV (High Definition Television) has been performed in addition to an ordinary SDTV (Standard Definition Television). Execution of the digital terrestrial broadcasting is also being examined.
In such an MPEG2 system, the CAT system is adopted as a process for limited reception. Keys for the limited reception have a triple-layer structure comprising a master key, a work key, and a scramble key. The work key is updated in a relatively long period, encrypted by the master key, and transmitted in the section format as an EMM (Entitlement Management Message) packet. Encrypted personal contract contents have been described in the EMM. Scramble key information is encrypted in a relatively short period and transmitted in the section format as an ECM (Encryption Control Message) packet. The PID with which the EMM is transmitted is designated by a limited reception descriptor in the CAT (Condition Access Table). The PID with which the ECM is transmitted is designated by a limited reception descriptor in the PMT.
In the receiver, the CAT is received. By receiving the CAT, the PID of the EMM is notified. The EMM for the user himself which coincides with the individual ID (card ID) in an IC card is then received. Information of this EMM is sent to the IC card and contract contents are stored in the IC card.
When a desired program is received, the NIT is obtained, a channel list is searched from the NIT, and a carrier frequency at which a desired program is being broadcasted is obtained. When the carrier frequency of the desired program is obtained, a receiving frequency is set into the carrier frequency at which the desired program is being broadcasted. The PAT is obtained at the carrier frequency. Program information in each carrier and the PID of the PMT showing the contents in each program have been described in the PAT. The PID in which the PMT of the desired program has been described is obtained from the PAT. Components (video/audio) of the desired program and the PID of the ECM necessary for descrambling are obtained from the PMT.
To descramble the scrambling, the packet of the ECM is received and information of the ECM is sent to the IC card. Only when the decryption is permitted on the basis of the contract contents stored in the IC card, a decrypt key is returned from the IC card. The decrypt key and the PID of the components to be descrambled are set into a descrambler. The packet of each component of the desired program is descrambled by a descramble key.
The descrambled packet of each component is sent to a demultiplexer. The video PES packet and the audio PES packet for receiving the desired program are separated by the demultiplexer. The video PES packet and the audio PES packet are then decoded.
The CA system of the MPEG2 has been described in the following patent literature (JP-A-8-265723).
As mentioned above, in the MPEG2 system, the limited reception by the CAT is performed. The limited reception by the CAT is performed on the assumption that one program is monitored by one receiving system. Therefore, to simultaneously monitor and record a plurality of programs, a plurality of receivers and a plurality of CA systems which are necessary for monitoring them are needed.
For example, upon recording of what is called a back program (program in the same time slot on a different channel), a program which is being simultaneously broadcasted by another program is recorded while the user is watching a certain program. In such back program recording, it is necessary to simultaneously receive a plurality of programs. In the case of processing in such a manner that display screens of two reception programs are simultaneously displayed onto one display screen like “PinP”, it is necessary to simultaneously receive a plurality of programs.
In the limited reception by the CAT of the conventional MPEG2 system, when a plurality of programs are simultaneously received as mentioned above, it is necessary to make a plurality of monitor contracts. However, it is not practical to make a plurality of monitor contracts in order to simultaneously receive a plurality of programs.